This invention relates generally to oil well packers and more particularly discloses a single string well packer which is settable through a multitude of various functional modes and ranges.
Normally, a well packer is used in oil and gas operations to seal a zone above the packer from a zone below the packer in a well bore. For example, after a well casing has been set and the well has been logged, a packer is then lowered into the well and located at a selected depth. For a casing perforating operation and testing of a zone spanned by a particular stratum, one packer may be positioned at the top of the zone and another well packer may be positioned at the bottom of the zone. This isolates the zone for testing and production after perforation. Packers are likewise used in cementing and fracturing operations to isolate the zone of interest.
The types of well packers in general use today are usually restricted to a mechanical set packer, a hydraulic set packer or a wireline set packer. One of the primary requirements of a satisfactory well packer is that the packer may be placed in a desired location and selectively set into strong gripping and sealing engagement across the casing diameter so that the packer may support the pressure above and/or below the packer and in some instances, support the weight of a tubing string.
Another primary qualification of a good well packer is that the packer is easily movable in the well casing without premature setting of the gripping members or the elastomeric packer elements before the desired zone is reached. Likewise, a preferable characteristic of a good well packer is that the packer has easy and predictable retrievability to prevent having to mill out the packer when an open casing is desired.
One particular well packer which has been utilized effectively under the conditions above is that disclosed in U.S. Pat. No. 3,714,984 to Read and assigned to the assignee of the present invention. This packer utilizes two unitary tubular gripping members to grip the well casing and provide longitudinal compression of the elastomeric elements to force them into radial expansion and sealing engagement against the casing wall.
A second patent, U.S. Pat. No. 3,818,987, to Ellis and assigned to the assignee of this invention discloses a well packer which has a selectively retrievable feature making it particularly advantageous for use under many well conditions.
A third well packer is disclosed in U.S. Pat. No. 3,804,164 to Ellis and assigned to the assignee of the present invention. The third packer utilizes a pair of unitary tubular gripping members and further features a hydraulic setting mechanism associated therewith.
Other U.S. Pat. Nos. such as 3,731,740 to Douglas and 3,548,936 to Kilgore et al also disclose well packers utilizing unitary tubular gripping members and having setting mechanisms falling within either hydraulic, wireline, or mechanical ranges. The present invention is thus an improvement over the above noted patents in that it provides all of the features and advantages found therein plus the additional desirable features of a preset indicating function and the ability to take up from both directions. In addition to these additional advantages, the mechanically set version of this invention offers an additional feature of having a shearably mounted upper gripping member.
The ability to take up from both directions is advantageous in that pressure above or below the tool generates forces which are carried through the upper and lower gripping members respectively and increases the compressive force on the packing element, thereby increasing its sealing effectiveness. The prior art packers are adapted to take up in one direction only and pressure occurring from the opposite direction in the well bore tends to decompress the packing element and lower its sealing effectiveness.
The preset indicator function provides a means when going in the hole in the mechanical set orientation to determine if the tool has inadvertently begun to prematurely set while running in the hole. In a premature set, the downward movement of the tubing string into the borehole may cause the packer to enter a series of irreversible steps such that the packer may not be subsequently lowered or raised in the well until it has been completely set, retrieved, and redressed at the surface. Redressing involves replacing the frangible elements and any damaged seal rings or packer elements.
The present invention avoids the premature set by the provision of a preset indicator function which involves a rotation of the upper slip into engagement in the well bore with a subsequent pause before setting of the remaining packer assemblies occurs. The indication of the weight indicator at the surface discloses that the setting operation has begun and gives sufficient time to reverse the direction of the tubing travel in the well bore before the irreversible portion of the setting operation has begun.
Thus, the present invention discloses a single string well packer utilizing dual unitary tubular gripping members, which well packer offers the advantage of full versatility in setting operations, full retrievability, and the advantages of a preset indicator and take-up from both directions.